It is known to provide a drain pump in an air conditioner in order to discharge drain water generated in a heat exchanger during cooling operation, draining operation, and the like. Such a drain pump is built into a ceiling embedded type air conditioner 1 as shown in, for example, FIG. 14, FIG. 15, and FIG. 16. Here, FIG. 14 is an external perspective view of the air conditioner 1 (ceiling is not shown). FIG. 15 is a schematic side cross sectional view of the air conditioner 1, and is a cross sectional view taken along the A-A line in FIG. 16. FIG. 16 is a schematic plan cross sectional view of the air conditioner 1, and is a cross sectional view taken along the B-B line in FIG. 15.
The air conditioner 1 comprises a casing 2 that internally houses various constituent equipment, and a face panel 3 disposed on the lower side of the casing 2. Specifically, the casing 2 of the air conditioner 1 is disposed so that it is inserted in an opening formed in a ceiling U of an air conditioned room. Furthermore, the face panel 3 is disposed so that it is fitted into the opening of the ceiling U. Principally disposed inside the casing 2 are: a fan 4 that sucks air inside the air conditioned room through an inlet 31 of the face panel 3 into the casing 2, and blows the same out in the outer circumferential direction; and a heat exchanger 6 disposed so that it surrounds the outer circumference of the fan 4. In the face panel 3 are formed: an inlet 31 that sucks in the air inside the air conditioned room; and outlets 32 that blow out the air from inside the casing 2 into the air conditioned room.
A drain pan 7 for receiving the drain water generated in the heat exchanger 6 is disposed on the lower side of the heat exchanger 6. The drain pan 7 is mounted to the lower part of the casing 2. The drain pan 7 comprises: an inlet 71 formed so that it communicates with the inlet 31 of the face panel 3; outlets 72 formed so that they correspond to the outlets 32 of the face panel 3; and a drain receiving groove 73 formed on the lower side of the heat exchanger 6 and that receives the drain water. In addition, a bell mouth 5 for guiding the air sucked in from the inlet 31 to the impeller 41 of the fan 4 is disposed in the inlet 71 of the drain pan 7. Further, a drain pump 308 that discharges the drain water collected in the drain receiving groove 73 out of the casing 2 is disposed in the portion of the drain receiving groove 73 of the drain pan 7 where the heat exchanger 6 is not disposed (specifically, between the outlets 72). The drain pump 308 is connected via a discharge pipe (not shown) disposed outside of the casing 2.
As shown in FIG. 17, such a drain pump 308 principally comprises: a pump casing 81 comprising a drain inlet 81a at the lower end part and a drain outlet 81b at the side part; an impeller 382 disposed inside the pump casing 81 and capable of rotating about a shaft part 91 extending in the vertical direction inside the pump casing 81; and a motor 83 disposed on the upper side of the pump casing 81 and that rotationally drives the shaft part 91 of the impeller 382. A motor fitting 89 for affixing the drain pump 308 to the casing 2 of the air conditioner 1 is mounted on the side surface of the motor 83. Here, FIG. 17 is a side view of the conventional drain pump 308 (depicting a cross section of the pump casing 81). In addition, the rotational axis line of the shaft part 91 of the impeller 382 is the P-P line.
The pump casing 81 principally comprises: a casing main body 84 comprising an opening at the upper part and disposed so that it surrounds the sides of the impeller 382; a casing cover 85 disposed so that it covers the opening of the upper part of the casing main body 84; and a sealing member 86 for sealing the space between the casing main body 84 and the casing cover 85. The casing main body 84 comprises: a cylindrically shaped main body part 84a whose diameter decreases in the downward direction; a tubular shaped suction part 84b comprising a drain inlet 81a at the lower end part and extending downward from the lower end part of the main body part 84a; and a tubular shaped discharge nozzle part 84c extending sideways from the drain outlet 81b formed at the side part of the main body part 84a. As shown in FIG. 16, one part of the discharge nozzle part 84c passes through a side plate of the casing 2 of the air conditioner 1. The casing cover 85 principally comprises an air introduction part 85a comprising a through hole substantially at the center that communicates with the atmosphere and the inside of the pump casing 81.
As shown in FIG. 18 and FIG. 19, the impeller 382 principally comprises: the shaft part 91 coupled to the drive shaft of the motor 83; a main blade 392 disposed inside the main body part 84a; an auxiliary blade 94 disposed on the lower side of the main blade 392; and a disc shaped dish part 93 disposed between the main blade 392 and the auxiliary blade 94, and having an opening 93a comprising an annular through hole at the center. Here, FIG. 18 is an enlarged view that depicts the vicinity of the pump casing 81 of FIG. 17. FIG. 19 is a plan view of the conventional drain pump 308 (the motor 83 and the casing cover 85 are not shown).
The shaft part 91 passes through the inside of the air introduction part 85a, and is disposed so that a gap is formed between the outer circumferential surface of the shaft part 91 and the inner circumferential surface of the air introduction part 85a of the casing cover 85.
The main blade 392 comprises, for example: four first blades 395 extending radially from the outer circumferential surface of the shaft part 91; and four second blades 396 extending radially from the outer circumferential edge part of the opening 93a of the dish part 93, and disposed between the first blades 395 in the circumferential direction. The height position of the upper end part of each first blade 395 (hereinafter, the height of each first blade 395 and each second blade 396 from the upper end surface of the opening 93a to the upper end part is defined as a blade height H1, as shown in FIG. 18) is the same height from the inner circumferential part to the outer circumferential part thereof. In addition, the blade height H1 of the upper end part of each second blade 396 from the inner circumferential part to the outer circumferential part thereof is the same height as each first blade 395.
The dish part 93 is disposed along a reduced diameter portion of the main body part 84a, and the annular partition part 93b extending upward from the outer circumferential edge part thereof is disposed so that it couples with the outer circumferential edge part of the main blade 392. The upper end part of the partition part 93b is disposed at a position lower than the upper end part of the main blade 392 (hereinafter, the height from the upper end surface of the opening 93a to the upper end part of the partition part 93b of the dish part 93 is defined as a dish height H2, as shown in FIG. 18). In other words, the upper end part of the main blade 392, viewed from the side of the impeller 382, protrudes more on the upper side than the upper end part of the partition part 93b. In addition, an external dimension D of the partition part 93b is substantially the same or slightly less than the outer diameter of the main blade 392. The auxiliary blade 94 is disposed inside the suction part 84b, and comprises four blades extending radially from the outer circumferential surface of the shaft part 91.
The impeller 382 of the drain pump 308 so constituted rotates in a prescribed direction when the motor 83 is driven. In so doing, a part of the suction part 84b is submerged to a point lower than the water surface of the drain water collected in the drain receiving groove 73 of the drain pan 7, and the drain water collected in the drain receiving groove 73 is consequently sucked in from the drain inlet 81a by the auxiliary blade 94, rises inside the suction part 84b, and reaches the main body part 84a. Further, the drain water that reaches the main body part 84a is boosted by the main blade 392, and then discharged from the drain outlet 81b via the discharge nozzle part 84c to the outside of the casing 2 of the air conditioner 1. Specifically, the drain water discharged from the drain outlet 81b is discharged via the discharge pipe disposed outside of the casing 2 and connected to the discharge nozzle part 84c. Here, the water surface that rose to the main body part 84a is substantially vertically divided into parts by the dish part 93, the flow of the drain water is partially blocked so that the flow is limited, and the drain water that contacts the main blade 392 is discharged (e.g., refer to Japanese Published Patent Application No. H10-115294, 2000-80996, 2000-240581, and 2001-342984).
Moreover, the discharge flow rate can be regulated by the water level h (refer to FIG. 18), without the drain pump 308 starting and stopping. In other words, the drain pump 308 is constituted so that the discharge flow rate decreases if the water level h falls, and the discharge flow rate increases if the water level h rises. Further, if the water level h rises to a certain water level and reaches the maximum discharge flow rate, then the discharge flow rate will no longer change even if the water level h rises further than that. Consequently, even if the amount of drain water generated in the heat exchanger 6 varies, stable operation is performed with a water level that balances the amount of drain water generated with the discharge flow rate.
Here, as the water level h inside the main body part 84a of the drain pump 308 falls, an air layer expands (refer to an air-liquid interface X in FIG. 18 and FIG. 19) circularly concentric with the shaft part 91 of the main blade 392, which consequently decreases the effective area by which the main blade 392 can perform the work of supplying water, and reduces the discharge flow rate of the drain pump 308. Conversely, if the water level h rises, then the air layer shrinks, which consequently increases the effective area by which the main blade 392 can perform the work of supplying water, and increases the discharge flow rate of the drain pump 308. Thus, the conventional drain pump 308 is structured so that the discharge flow rate can be regulated by the water level h.
In addition, the back pressure may decrease depending on, for example, the installation conditions (piping length, inner diameter, height, etc.) of the discharge pipe connected to the drain outlet 81b. In such a case, the head of the drain pump 308 decreases, which consequently expands the air layer circularly concentric with the shaft part 91 of the main blade 392.
Compared with a pump of a type wherein an impeller is generally submerged completely, such a drain pump 308 is constituted so that the air-liquid interface between the air and the water is formed at a portion where the main blade 392 is disposed; consequently, the pump efficiency is low and the operating noise is loud. Further, this operating noise is generated principally by the agitation of the air layer by the main blade 392, and the air layer acceleratedly increases the more it expands on the outer circumferential side of the main blade 392. Particularly when the head is low, the air-liquid interface between the air and the water (refer to an air-liquid interface Y in FIG. 18 and FIG. 19) expands to the outer circumferential part, where the circumferential velocity is high, which consequently generates an extremely loud operating noise. This operating noise becomes a problem particularly if the flow rate of the fan 4 of the air conditioner 1 is low, or if the inside of the air conditioned room is quiet.
In contrast, with the aim of reducing the operating noise by making the air-liquid interface Y above the upper end part of the partition part 93b flow smoothly, it is also known to employ the impeller 382 provided with inclined parts 395a, 396a at the outer circumferential part of the main blade 392 (specifically, the first and second blades 395, 396) only at the portion on the upper side of the upper end part of the partition part 93b (i.e., the portion between the blade height H1 and the dish height H2), as shown in FIG. 20; however, even in this case, the operating noise cannot be sufficiently reduced.